PBR dielectric material in luxrender?
I believe the Glossy material type in luxrender does what you want out of the box.

Unlike the glossy shader in cycles, the luxrender glossy material includes a "matte" component (diffuse in cycles-speak), making it loosely analogous to the following cycles setup:



Luxrender glossy node for reference:





Render comparison

Cycles


Luxrender


I'm not really sure why the cycles render is dimmer than the luxrender example in this case. The difference appears to be in the diffuse part of things. If someone knows what's going on here, I'd definitely like to hear about it